Protective device



March 23, 1943. C. RCRAIG PROTECTIVE DEVICE Filed Oct. 14, 1941 47 Inventor; Chaudes F. @Ta/cg.,

His Attorney.

Patented Mar. 23, 1943 UNITED STATES PATENT OFFICE 2,314,346 y PROTECTIVE nevica Charles B.. Craig, Pittsfield,

General Electric Company,

New York Mass., assigner to a corporation of Application October 14, 1941, Serial No. 414,917 '7 Claims. (CL 20o-120) My invention relates to protective devices and more particularly to fused protective devices for protecting electrical apparatus of the liquid insulation filled type, such as transformers and the like, where the fused protective device is mounted within the casing of the electrical apparatus. Specifically, my invention relates to protective devices of the type disclosed and claimed in` United States Letters Patent 2,223,232, granted November 26, 1940, upon an application of S. R.

` Smith, and assigned to the same assignee asthe present application. v

It is an objectof my invention to provide a new and improved fused protective device for electrical apparatus 'which is simple and sturdy in construction and relatively inexpensive.

It is another object of my invention to provide an improved fuse device and mounting therefor.

, the mounting arrangementA of the fuse device of Fig. 1 with respect thereto, and Figs. 2, 3, and 4 are sectional views of modifications of the fused protective device of Fig. 1.

Although my invention may be employed in 4the protection of forms of'electrical apparatus other than transformers, such as, for example, capacitors, where similar problems may be encountered, I have elected for the ypurpose of describing and illustrating my invention to show it as applied to the protection of an electric translating apparat such as a transformer.4 In Fig. la of the drawing, I designates an electricl translating'apparatus, such as a transformer,

only a portion of whichgis shown to illustrate the internal assembly of the translating device with particular relationship to the fused protective device to be described hereinafter. It should be understood that the particular construction of the transformer has no bearing on thepresent invention and is merely schematically shown for the purpose of illustrating my invention. The interior of the transformer casing is preferably filled or substantially filled with a liquid insulation II, such as oil, or a liquid halogenated hydrocarbon composition, suchas is described and claimed in United States Letters Patent 1,931,373, `granted upon an application of F. M. Clark, and assigned to the same assignee as the present application. Immersed in the insulating liquid are the transformer windings, not shown,

the transformer core I2, and a core-clampingl framework I3. Fuse devices of the present invention are particularly adapted tobe supported within the transformer casing submerged or at least partially submerged in the body of liquid dielectric II and connected in series with one s et of transformer leads. Although Fig. la shows only one of the fuse devices, generally indicated at I4, connected in one of the leads of the transformer, a plurality of devices may, if desired, be so connected where taps or seriesparallel connections are employed.

In transformer constructions made heretofore,

Athe core-clamping structure or framework I3 often supports an insulating member or support of some sort such as I5 in Fig. la, which is particularly adapted to ,support the fusedevice Il of the present invention.

Referring now to Fig. 1,the fuse device Il comprises a tubular casing formed of a metallic arc chamber I6 of relatively large volume, which is constructed of a material adapted to withstand high pressures, and an insulating cylindrical member I6. The insulating cylindrical member I6' is threadedly mounted in one end of are chamber I6 so as to complete the tubular casing for the fuse device I4. 'I'he other end of arc chambery I6 is provided with a tubular extension I1 of reduced diameter which, asis shown in the drawing is preferably integrally formed with arc chamber I6. Tubular extension I1 also has a depending portion I8 which extends for a short distance into arc chamber I6 in Fig. l. Insulating cylindrical member I6 is preferably formed of an insulating material from which gas is evolved when subjected to the heat of an electric arc or, if desired, insulating cylindrical member I6' may be formed of a suitable insulating material lined with a. gas-evolving material. Mounted within the tubular casing of fuse device I4 is a fuse link, generally indicated at I9, which is preferably of the well-known buttonhead type. Fuse link I9 comprises a short fusible section mounted within arc chamber lIii and includes a strain wire 20 and a fusible link 2|. The buttonhead 22 of fuse link I9 is clamped ,into position against the end of tubular extenconductor 2l is electrically connected to terml- 10 nal nut 26 as at 2l. External electrical connections with terminal nut 26 may readily be made as at 29. Preferably. these external connections are mode diametrically opposite the connection with the Iuse link 28 so that they may be completed without disturbing fuse link i9.

The fuse device Il is preferably submerged in the body of dielectric il so that the maior portion of arc chamber Ii is below the liquid dielectric level or it may be completely submerged as indicated in Fig. 1a. In this manner, the arc chamber i6, within which the fusible section of fuse link I9 is placed, provides a very large volume of liquid dielectric to cool the arc which .forms upon rupture of the fusible element.

In order to allow the liquid dielectric to rise into fuse device I4 almost to fill it and surroundthe fuse link I5 including the fusible section 2i and strain wire 20, a suitable vent 3l is provided in the wall of arc chamber I6 opposite the bottom end of depending portion I8 so that contained air may escape as the liquid rises to the level of the air vent after which air will be trapped above the liquid level inside chamber i8 and around the depending portion i8. Air Will also be trapped in tubular extension i1 but, should closure member 23 be removed for replacement of fuse link il and the air in tubular extension i1 displaced by liquid, the trapped air inside chamber ii above vent 3U and surround- 40' ing depending portion i8 willremain, the purpose of this trapped air being to help cushion the irnpulse shock resulting from current interruption by the fuse device. Vent 3l is suiliciently small .so that substantially no liquid can escape therethrough in the short interval of time during arc .interruption and, therefore, the pressure built up in arc chamber ii is maintained to force liquid.' fuse parts, and the arc out through insulating cylindrical member ii", thereby facilitating cooling of the arc `and interruption of the curl rent inthe circuit.

In order to support the fuse device Il in the position indicated in Fig. la, I provide a pair of insulating nuts v3i and 32 vwhich are threadedly mounted Lon insulating cylindrical member i6', Insulating nut 3i ,is mounted above Support ii while insulating nut 32 is mounted below support l5 to support .fuse device il rigidly in the posiinon indicated in Fig. la, the insulating cylindiical member ii' extending through an opening i5' in insulating lsupport i5.

From the above description, it will be obvious that I have provided a fuse device with Simple member 3l as by set screw 35 threadedly mounted in the lower end of housing member 33. External electrical connections may be made with the lower end of fuse device Il by connection with metallic housing member 33 as shown at Il.

Although in Figs.. 1 and 2, I have indicated aiusedeviceinwhichthearcchamberll adapted to `withstand high pressures comprises only the portion ot tubular casing Il within which the fusible section of fuse link il ismoimted, it may be desirable that all o! the tubular casing be made sufficiently strong to withstand the high pressures and, accordingly1 in Pig. 3, I have illustrated a modication of my invention in which a metallic cylindrical member 31 provides an arcing chamber 3l at the upper end thereof similar to the arcing chamber Il oi' Pigs. 1 and2. Atubularinsulatingmcmberllis threadedly or otherwise mounted within metallic cylinder 31 which reenforces the insulating tubular member 3l and the two members Il and supporting means permitting ready removal and replacement of the device when desired.

Since the fuse device .Il isusually used inside the tank or casing of 'liquid lled electrical apparatus, such as transformers, it may be desirable to provide means for catching the molten or 7o solid metallic parts of the. fuse link blown out of the tubular casing `upon operation of the fuse device. In Fig. 2, the fuse device I I of Fig. 1 is shown with the corresponding parts thereof designated by the same reference numerals as in Fig. Il

Ilformthetubularcasingofthe'tusedevice of Pig. 3. Metallic cylinder Il is provided with an extension Il ofreduced diameter for cooperatingwiththebuttonheadl! ofafuselink inthesamemannerastheconstructionshown inFig. 1. Asuitableendclosurememberllis tbreadedly mounted on tubular extension Il to cmnpthebutmnheed u ufruseunku mm puatlon. The fusible section including strain wire 4i andfnsiblelinkotfuselinkllisan'mged tobewithintheportion of metallic cylinder Il of relativelylargevolume above insulating cylindricalmember. Asuitableilexibleconductor llformsthelowerendotfuselinklndis electrically connected to a suitable lower terminal,notshown. Aventllisprovidedinthe ilxgerglularextensionliofmetallic cylinder or Pillflleofallowing trappen intnecylinderto www mum my lise .im n un. theiuselinkll. Theiusedecellmaybempported on an insulating member Il, having an opening i5' therein through which 'the tubular singofthefusedevicemayextendbymenm ofanannularmemberwhichmaybebnnd clamp supporting memye memberandnutil. Inordertoprevmthot gasesandthelikeexpelledtromthelowerendof lthetuhularcasingoffusedevicellfrom in contact with metallic cylinder ll and nut il. Iprovideaninsulating cup-shapedmembail ihreeriy moimted on cylindrical mem whichextendsbelowtheremforcing meAtalliccylinder-U.

modiilcation of the supporting means ot HgJisshownlnFigAinwhichthefmedevice merals used in Fig. 3. r In this case, yan insulating cylinder or bushing 52 having an opening I5 therein extends through hole I" in supportl I5 with metallic cylinder 31 clamped as shown by means of annular member 49 and nut 50 to support fuse device 40 in the same manner as in Fig. 3. yA terminal nut '54. not shown in Fig.3, is threadedly mounted on the end of insulating cylindrical member 39 extending below metallic cylinder 31 to which the ilexible conductor 41 of fuse link 43 is electrically connected as at 55. Electrical connections to the fuse device 40 may be made at 55 and 56 as shown in Fig. 4.

While I have shown and described particular embodiments of my invention, it will be obvious is designated by the corresponding reference nu- Y to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a fuse device of the type at least partially submerged in a liquid dielectric. a tubular casing including an -arc chamber of relatively large volume constructed of a material adapted to withstand high pressures. a fuse link in said casing including a fusible section located in said arc chamber, closure means for the top end of said casing, and means defining a small air vent 'near the top end of said casing for permitting air to escape from said casing to allow the liquid dielectric to rise in said casing to surround said fusible section to a 'level above which a predetermined amount of air will be permanently trapped to cushion the shock resulting upon operation of said fuse device.

2. In a fuse device of the type at least partially submerged in a liquid dielectric, a tubular casing including at one end thereof an arc chamber of relatively large volume constructed of a material adapted to withstand high pressures, a fuse link in saidcasing including a fusible section located in said arc chamber, closure means for the arc chamber end of said casing, means cushion the shock resulting upon operation of said fuse device.

3. In a protective device for electric apparatus of the type having a body of liquid insulating dielectric, the combination of an insulating support, a tubular casing, means for mounting said tubular casing on said insulating support so as to be at least partially submerged in said body of dielectric, a fuse link in said casing, closure means for the top end of said casing, and means defining a small yair vent near the top end of said casing for permitting air to escape from said 'casing to allow the liquid dielectric to rise in said casing to surround said fuse link, said vent being sulciently small that substantially no liquid can escape therethrough in the short interval of time during rupture of said fuse link and consequent circuit interruption.

4. In an electric apparatus, the combination of an insulating support, a protective device comprising a fuse link including a fusible section, an arc chamber for the fusible section of said fuse link, a. body of liquid dielectric, said arc chamber having an opening at the bottom thereof for receiving said liquid dielectric, said fuse link being so disposed in said arc chamber as to be immersed in said body of dielectric, closure means for the top of Said arc chamber, and means deflning a small air vent near the top of said chamber for permitting air to escape from said casing to allow the liquid dielectric to rise in said chamber to a level above which a predetermined amount of air is permanently trapped to cushion v the shock resulting upon operation of said fuse device.

5. In a fusedevice of the type at least partially submerged in a liquid dielectric, a tubular casing including an arc chamber of relatively large volume constructed of a material adapted to withstand high pressures, a fuse link in said casing including a fusible'section located in said arc chamber, closure means for the top end of said casing, means defining a small air vent near the top end of said casing for permitting air to escape from said casing to allow the liquid dielectric to rise in said casing to surround said fusible section to a level above which a predetermined amount of air will be permanently trapped to cushion the shock resulting upon operation of said fuse device, and means for completing external electrical connections to said fuse device without disturbing said fuse link.

6. In a protective device for an electric translating apparatus of the type having a body of liquid insulating dielectric, the combination of an insulating support, a tubular casing, means for mounting said tubular casing on said insulatf ing support so as to be at least partially submergedv in said body of liquiddielectric, a fuse to rise in said casing to surround said fusible section, external electrical connections for said protectivevdevlce, and means for replacing said fuse link without disturbing said external electrical connections.

'1. In a fuse device of the type at least partially submerged in a liquid dielectric, a tubular casing including an arc chamber of relatively large volume constructed of a material adapted to` withstand high pressures, a fuse link in said casing including a fusible section located in said arc chamber, closure means for the top end of said casing, means defining a small airvent near the top end of said casing for permitting airto escape from said casing to allow the liquid dielectric to rise in said casing to surround'said fusible section to a level above which a predetermined amount of air will be permanently trapped to cushion the shock resulting upon operation of said fuse device, and means associated with said casing for catching the molten or solid metallic parts of the fuse link blown out of said casing upon operation of said fuse device.

CHARLES R. CRAIG. 

